so basically someone over there did boot a xs3.1 just fine with macpro 5.1 140.0 firmware but he lost hardware xserve fonctionality such as led planel on front here is what he say :

Here it is ... Hope that can help, I already flashed it with a MacPro 5.1 even with boot room 140.0 booted fine showed as a MacPro 5.1 and I could put 6 core and 12 core same thing as the Mac Pro. Now you lose the Hard Drive led's activity, and the front panel led too, so I did revert back to Xserve original rom 2009, Installed Sierra, and High Sierra on the other, Got back the LED HD's activity nice I love it, and I managed also to bring back the LED front Panel ... Where It used to be a time where the front panel was working OOB under the Snow and Lion 10.7.5 era with Server install, but I found a way to run the LED's even under ML, Mavericks and UP to High Sierra...

so i don’t understand if he had remove the 6 core and put back the 4 core to boot into xs3.1 firmaware, or if reverting to x3.1 actually kept the processor compatibility....pending on his reply...

So with IceQ problem is.... fans full on (because I guess in Windows it is say no reading temperature which shows 0 degree) - but I got Apple Boot Logo and works great in macOS and Windows - just fans full on - no matter if with UEFI or without.

Then I got BIOS from...... my other IceQ (same looking and same model) but with little bit different CRC checksum - and... fans become quiet on this BIOS - ....... BUT it does not boot to macOS - and to be more crazy - it is booting to Windows! And again - does not matter if with or without UEFI.

At the moment I've stuck with BIOS switch 1: Apple Boot Logo and fans full on and BIOS switch 2: quiet fans BUT able to boot to Windows only.

i am kindly asking your help as i yesterday tried first time flashing graphics card on mac pro and miserably failed.

proceeded the following way:

MacPro1.1 > in Bootcamp in Downloaded "GPU-Z" and saved current ROM from card 5770 ("Juniper.rom") > from Macrumors trusted member i "found" .Rom which supposedly function for this port mapping with 2xDVI/HDMI/DP - downloaded .rom ("5770e2.rom or similar) > in Bootcamp i downloaded WIN ATIFLASH > loaded .ROM and flashed

after reboot the card is no longer seen by macpro, neither in bootcamp nor in osx.it could be that the .ROM i was using was meant for 64-BIT MacPro? or why else it could fail?

How could i now reflash the card with only having the MacPro 1.1/2.1 and no proper PC with integrated graphics or with 2 fullsize PciE Lanes Available?

JWith the latest EFI firmware update for the Mac Pro 5,1, you will get 5GT/s without having to do any resistor mod. The Mac Pro 1,1 is limited to PCIe 1.0, I believe, so your max throughput is 2.5GT/s regardless.

I just have the MP (1.1)2.1 left, and am awaiting an R9 280 (unflashed). so either way, with resistor mod or withouth, i will only get 2,5Gb/s?Then there is probably no need to risk the resistor mod, or are there any benefits?If i would flash the card (in my understanding only possible if someone is offering an EFI, or am i wrong?), would i get additional benefits , next to the bootscreens?